1. Field of the Invention
The present invention is generally related to a voltage comparison circuit with temperature compensation capability and, more particularly, to a circuit that utilizes the inherent temperature variation of the base-emitter voltage drop of transistors to regulate the feedback of a comparator and therefore change the hysteresis characteristics of the comparison circuit as a predictable function of temperature.
2. Description of the Prior Art
Voltage comparison circuits are used in many different applications that are well known to those skilled in the art. One application for voltage comparison circuits of this type is in a geartooth sensor that utilizes a plurality of magnetoresistors that are connected in a Wheatstone bridge arrangement. For example, four magnetoresistors can be arranged in a bridge configuration so that the voltage differential across the bridge is indicative of the presence or absence of a magnetic component, such as a geartooth, in a predefined detection zone proximate the geartooth sensor.
U.S. patent application No. 08/179,800 (M10-15537), which was filed by Wu on Jan. 11, 1994, describes a proximity sensor that provides two magnetoresistive elements that are disposed in a common plane and displaced from a lateral surface of a permanent magnet. The common sensing plane of the magnetoresistive elements extends in a direction generally parallel to a magnetic axis of a permanent magnet that extends between the north and south poles of the magnet. A detection zone is defined relative to a preselected magnetic pole face and the magnetoresistive elements provide first and second signals that can be compared to define a third signal which is representative of the presence or absence of the magnetically permeable object within the detection zone. The magnetoresistive element can each comprise a plurality of magnetoresistors which are arranged in a Wheatstone bridge configuration for the purpose of providing the first and second signals described above.
U.S. Pat. No. 4,506,217, which issued to Rothley et al on Mar. 19, 1985, discloses a geartooth position and speed sensor with four magnetic resistance tracks. In order to simplify a speed and position sensor, four meander-arranged permalloy resistance tracks are located on a substrate at the corners of a rectangle. They are spaced in circumferential direction by approximately half the pitch distance of the teeth of a starter gear. The resistances can be connected in a voltage divider configuration or in the form of a bridge circuit supplied from a constant current source to eliminate temperature variation effects.
When a magnetic sensor is used to detect the presence or absence of a magnetic object within its detection zone, it is very important that the sensor's ability to identify the position of a geartooth is not adversely affected by changes in temperature. When a geartooth sensor is utilized in automotive applications, the large temperature range under which the sensor must function can present severe problems. These problems are particularly troublesome in automotive applications because changes in temperature may change the sensor's ability to determine the precise position of a rotating member that is required for proper timing and operation of the automotive engine.
It would therefore be significantly beneficial if a voltage comparison circuit could be provided which changes its own operation characteristics in response to changes in temperature so that the precise position of a rotating gear can be determined accurately throughout a large temperature range.